As is known, units for supplying fuel to the combustion chambers of an endothermal engine comprise a fuel manifold, within which the fuel to be supplied to the combustion chambers is stored, one or more injectors connected to the fuel manifold and adapted to supply, on command, a predetermined quantity of fuel to each combustion chamber, a fuel storage tank and a high pressure pump adapted to take the fuel from the storage tank in order to supply it at high pressure into the fuel manifold.
These supply units further comprise a pressure regulator of proportional type disposed on the fuel manifold in order to prevent the pressure of the fuel in the fuel manifold from exceeding a predetermined threshold value, and a recycling duct connecting the pressure regulator to the intake of the pump in order to convey, upstream of this pump, the surplus fuel that the pressure regulator draws from the fuel manifold.
The pump generally has a body provided with at least one cylindrical seat within which a respective piston can move axially between a forward position and a retracted position in order to define, at the location of an end zone of this cylindrical seat, a variable volume pumping chamber. The intake of the volumetric pump is connected to the storage tank in order to suction fuel into the pumping chamber, while the outlet of the pump is connected to the manifold in order to supply the fuel at high pressure to this manifold.
The piston is generally provided with an annular sealing gasket, which is disposed at the location of a central portion of this piston and is adapted to ensure that the connection between the piston and the cylindrical seat is fluid-tight.
Unfortunately, during operation of the volumetric pump, because of play due to an imperfect coupling between the piston and the cylindrical seat in which it is mounted, there may be leakages of fuel from the pumping chamber towards a zone of the cylindrical seat disposed below this chamber. In particular, the fuel that leaks strikes the lateral surface of the piston and, as it is at high pressure, exerts a stress on the gasket which may in the long term cause it to deteriorate. The leaked fuel may therefore flow outside the body of the pump and come into dangerous contact with the lubrication oil circuit or even with the engine components in the vicinity of the pump.